According to Piper Jaffray analyst Gene Munster, Google could earn $1.3 billion in mobile advertising revenue in 2012, or $9.85 for each Android user. The analyst forecasted there would be 133 million Android users by 2012, and he arrived at the $1.3 billion figure by using publicly quoted numbers from Google itself.

The details of Munster's prediction can be found on eWeek, Forbes, CNN and other outlets. Munster had posted this information in a research note earlier this week.

To determine the $1.3 billion figure, the analyst used Google's self-stated figure that its mobile ad business is on a $1 billion annual run-rate, and Munster estimated the company had earned $850 million in total mobile revenue in 2010. Android specifically had generated around 16% of that total, or $130 million, said Munster. That means that each Android user generated $5.90 per year for Google, based on around 22 million Android users in 2010.

By 2012, there would be 133 million Android users, generating $1.3 billion in Android-related revenue he said. That equates to $9.85 per user per year.

Mobile Still Pales Next to Desktop Web

Despite this growth, Piper notes that even an ARPU (average revenue per user) of nearly $10 is still below what a desktop user generates for Google.

"As we noted, we believe Google's ARPU on Android was $5.90 in 2010. We believe Google's average revenue per search user was $18.85 in 2010 and average revenue per user for Google's advertising businesses in total was $25.77 in 2010," Munster said.

Below is a chart which shows just how far Android has to go before catching up to the desktop Web.